Degreeing cams

And that too is changing. Their younger generations are much more "westernized" in their corporate thinking. More, "whats in it for me" and less "all for the company" attitudes. Take a look at Toyota's quality problems over the last decade.

 

What a great thread!
I have a couple of questions:

- to do all the valve opening and closing points verification work you need to have the belts on, of course, but to re-pin the cams you need to remove them, right? Do you use the old belt to do it and when everything is perfect just replace by the new belt?

- if you need to re-pin the intake cam in one direction and the exhaust in the other direction, won't that interfere with the belt teeth alignment between the two?

Thanks! I'm about to do it in my 328 next weekend ...

 

Uhhhhh, there is an ocean of difference between the quality of parts and the mechanical fortitude of the people who assemble things. Helicopters are so dynamic, with so many high energy forces working in so many directions at the same time, it only takes one error of assembly to let the whole thing come unglued.

A hovering helicopter would be comparable to running a Ferrari around in a hard circle at 90% of full power, continuously. The first part that breaks will stop the ride, but the results will be much less dramatic. The more I know about Helicopters, the more I want to stay away from the damned things.

 

LOL! Isn't that true. The scariest ride in the air of my life (that includes thunderstorms, near mid-airs, bird strikes, etc) was in an Army helicopter. I was cargo in a Crash-hawk and watched as screws unscrewed themselves from the ceiling and dropped at my feet. Repeatedly. When I glance over at the crew-chief he just smiled. Never freakin' again.

 

You install "new" belts, set the belt tension, then set about degreeing. You have the pulley bolts finger loose. You bring your crank around while watching you indicator, and note the opening. If your early or late, you pull that cams pin from the pulley and rotate that cam to a more correct position and note the pin holes, see if a hole is really close and shove the pin in. If the holes are way off, you can slip the pulley off the cam, and if your careful, not upset the belt on the other sprockets. You rotate that cams pulley under the belt, and try to find a different position, a place where one of the pin holes better align. IIRC, someone once said there is a 3 degree variance between pin holes, so in reality you should be able to hit it +/- 1.5 degrees.

This all presumes the TDC register at the flywheel is correct. If its off any amount, everything, including ignition timing, will be off the same amount. I would always check for true TDC before moving on to valve timing. Once your timing is correct, rotate the engine several times and recheck it, and reset the tensioner. Put the locks on the cam bolts, tighten them down and lock them. I use an impact wrench to tighten them while securely holding the pulley in my hand to take up shock. I dont really know how you could apply the listed torque via wrench without some type holding fixture, but a good bump with the impact should be sufficient.

 

Go to youtube and type in "helicopter crash".

My dad and I took a heli ride at Mt Rushmore back in 74, left my mom back at the car. When we got back home a month later we heard it shed the main rotor blades and went down killing everyone aboard. I cant imagine what my moms reaction would have been, stuck in the middle of nowhere with a car she couldnt drive, waiting for us to never return. I guess it just never felt worth it after that.

I read once about an Army trained heli pilot instructor with over 15,000 hours. He was walking out to the heli one day and said something just said "no". He walked away and never looked back. His only answer was too many parts all trying to get away from each other, and its only a matter of time before they succeed.

Somebody else said they have the glide slope of an Anvil. They land like one too on occasion. Once.

 

Yes, but this is how the design is intended to work. By selecting the right holes on the cam AND by skipping the proper number of belt teeth, the adjustment resolution is 1 degree (so, in theory, you should be able to find a combination that puts you within +/- 0.5 deg of the target). The attached spread sheet shows how these two factors (using different pin holes and skipping different numbers of teeth) give 1 deg increments over a 12 deg range (+/- 6 deg) -- which is the range you need since each tooth on the belt is 12 degrees apart:
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Thanks for the clarification, I had it in my head it was 3, but that always seemed excessive.

 

Fantastic help, guys! I think I got it now.
What's the best method to rotate the cam while the pin is off? I'm thinking it could very well rotate on it's own because of the valves, so it can involve some force to put it where I want. On a 4 valve engine I don't have much space between the pulley and the head to use a vise-grip.

 

Its not going to harm anything if the cam snaps around on you, its only if you decide to TURN THE ENGINE afterwards. Just turn the cam back and youll be okay.

There should be enough room to get a pliers around the end of the cam, or perhaps your has flats for a wrench (spanner) on the cam, better yet. If using pliers you might care to wrap the cam with some cloth to protect it, but it should be fairly easy to turn the small amount were talking about (a few degrees this way or that).

 

On my 348, I used a pin in the back of the cam hole (not the gear), and used a screwdriver against it to rotate the cam. That's only easy on the 1-4 side, though, where there's more space between the gear and head. It was harder on the 5-8 side (much less room). Not saying it's best or easiest, but it worked. Use a hard pin... mild steel will deform based on the realtively thin diameter. Hope this helps.

Edit: now that I think about it, the pin I used wasn't full hole diameter, so that's also why the mild steel one I used deformed.

 

What do you guys think of this

http://www.tooltopia.com/innovative-of-america-7886.aspx

a friend is sending me some dial gauges and a degree wheel but I dont have anything that will measure TDC (PM)

Is this accurate enough??

 

""1/8" graduation marks""

Only if I dial indicator can accurately be placed on top of it. Measuring piston travel with a yard stick falls outside the realm of degreeing cams.

 

Nope...This set-up is one way to go. The dial indicator reading TDC, on each side of the arch, has 0.01mm resolution.
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Probably not well suited to the DIY user, but we've found this to be a very attractive option for shops:

http://www.ricambiamerica.com/product_info.php?products_id=284232

 

And a great, well-made and thought out product it is...!
Shameless plug: And that's what we're using in the above engine photos

 

Get a piston stop for $10 and be done with it.

http://www.summitracing.com/parts/SUM-900189/

I have a toolbox full of indicators, etc and I still think the piston stop is the best way to determine TDC.

 

too late.... Im trying to live up to Dave's expectations (and Enzo's) not sure I am smart enough or capable but I will do my best. Failure is not an option! I am also curious as my GT4 runs as well as any 308 I have ever seen so I am interested to see how close it was before adjusting. I will need more of all your help that is for sure.....
I cant find the spec for the reduced size shim needed does anyone know what that spec is in MM offhand?

Rob

 

Dear Freinds,

I just removed my cams again, so I guess Im going to attempt this. I am seriously going to need all of your help and advice. I know I can do this with your help so bare with my stupid questions.

My first few questions

1. I cant find in the WSM where it says to use a thinner shim to check the valve movement, what is the spec needed. I finally read between the lines to see where it says you should degree the cams.

2. I still cant figure out from reading all the posts what is the exact valve movement measurement, is it from the second the dial indicator shows the bucket is moving? Is that where on the degree wheel the valve event starts???

3. All my cams are out and I am still at TDC on my flywheel, using a degree wheel cant I turn the engine backwards and forwards a bit to determine true TDC?

4. THis may sound like a real dumb question , but I know I am at TDC as the cam caps were lined up when I removed the cams and never touched the crank. If you turned over the engine only once, putting it out of the original TDC and then re-installed the cams would they not be correct, even tough you were 360 degrees off the original TDC? I dont plan on doing this just trying to understand how this engine works.

Thanks to all in advance,

Rob
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I'll take the easy one.

Number 4. Yes but only if you remove all the cam shafts, turn over the crank 1 turn, and then reinstall all the cam shafts. Then it does not matter at all. The engine block is not smart enough to know what you have done.

 

The "spec" is given in the table on page B27 where it says:

Timing clearance 0,50 mm

(but see #2 for your options)

When the "event" occurs on the degree wheel depends on your test set-up:

A. If you use a thinner shim to set the clearance to the 0.5 mm, the "event" occurs when the shim starts (or stops) moving.

B. If you leave the valve clearance at the operating spec, the "event" occurs when the deflection of the shim + the measured operating clearance = 0.5 mm

C. If you use a thicker shim to set the operating clearance to zero, the "event" occurs when the deflection of the shim = 0.5 mm

(All three of those methods use the exact same point on the cam lobe to define the "event".)

Sure, this is how a piston stop works too. The slope of the piston motion curve is zero at TDC so it's better to measure when the pistion is down a bit on one side (slightly before TDC) and then down the same amount on the other side (slightly after TDC), and then call TDC the midpoint between those two measurements on the degree wheel.

 

Thanks Guys.

Im going to put my spline gear back n the repaired cam right now, wish me luck!

I guess then I am going to remove the bolts in the cams next and put them back where they were, as a starting point. Do you leave the o-ring out until the final torque. I seems taking it in and out might deteriorate it a bit???

Also when you find real TDC do you remark the plate on the flywheel or make a new one?

Rob

 

(IIRC) There should be some slop in the mounting holes so you should be able to move the reference plate (with the mark) a little after loosening the mounting bolts if you need to make a minor readjustment.